1. Field of the Invention
The present invention relates to an image processing device which performs white balance correction and color difference correction, an image processing method, and a non-transitory computer-readable recording medium for recording an image processing program.
2. Description of the Related Art
While a signal value of an analog signal can continuously change, a digital signal can change only by a predetermined quantization unit. Therefore, when an amount of change from an original signal value occurs, for example, in a luminance signal, a false contour may appear.
As a technique for reducing such a false contour, for example, Japanese Patent No. 4301627 describes a false contour correction technique in which a change corresponding to twice a minimum quantization unit of a video signal is detected as a bit loss part and is corrected to a change in the minimum quantization unit.
On the other hand, white balance processing for a color image has been conventionally performed as one of image processes. The white balance processing is processing for adjusting color balance so that a white part looks white by multiplying each color component by a different gain.
More specifically, in the white balance processing, for example, processing is performed in which some color components are multiplied by a white balance gain more than 1, and other color components are not multiplied by a white balance gain (or white balance gain by which the component is multiplied is 1).
However, when such white balance processing is performed, tone precision after the processing differs among color components, and a false color (a false color contour), which is color noise, may appear in gradation.
As a technique for reducing such a false color, for example, Japanese Patent Application Laid-Open Publication No. 2013-223061 describes a color noise reduction technique in which color difference data of image data for which each color component is multiplied by a white balance gain is calculated, and the color difference data within a color difference range where color noise in achromatic color gradation is conspicuous is reduced According to the technique described in Japanese Patent Application Laid-Open Publication No. 2013-223061, an effect of reducing coloring in achromatic color gradation can be expected, and an effect of deterioration of tone precision due to the white balance gain being improved can be also expected.
Some of recent digital cameras are provided with an image pickup driving mode capable of reading image pickup data at a high speed, and the digital cameras are used in a case of performing high-speed consecutive shooting or performing live view display at a high-speed frame rate enabling smooth motions. Such high-speed reading is achieved by reading low-bit image pickup data (that is, image pickup data with low bit precision).